Identification

Needles at the tips of the branches (current year needles) turn yellow

Pale orange to white tube-like projections appear on infected needles in July
or August and release powdery orange spores

Severely infected trees may have a tan to pinkish cast

Infected needles fall off in September

Some species of rust can cause witches' brooms, a clump of small weak
branches arising from one point on a large branch

Biology

The spruce needle rust fungi live half of their life cycle on spruce needles and
the other half on an alternate host in the Ericaceae family. In Minnesota labrador
tea (Ledum groenlandicum), leather leaf (Chamaedaphne
calyculata), and bearberry (Arctostaphylos uva-ursi) can all serve as
alternate hosts for spruce needle rusts. In the spring, spores are released from
the alternate host plant and infect young growing spruce needles if cool wet
weather is present. In the summer months, these infected needles develop spore
producing structures that release orange powdery spores. These spores can only
infect the alternate host plant and do not reinfect the spruce. Infected needles
often turn yellow and in most cases, fall off at the end of the growing season. The
fungus that causes witches' brooms in addition to needle infection can overwinter
within the infected spruce branches. All other spruce needle rust fungi overwinter
in the alternate host plant.

Management

In most cases spruce needle rust is a cosmetic problem and no management is
needed.

Reduce moisture on needles by redirecting lawn sprinklers away from spruce
trees and spacing spruce trees to allow good air circulation around the
tree.

If witches' brooms are present these can be pruned out and destroyed.

Removal of all alternate host plants within 1000 ft will reduce disease on
spruce but is often impractical.